How do we estimate the size of a population? Mark-recapture.
Capture and mark a smaller sample of the population, then re-capture and use this to estimate the total size.
Do populations grow fast or slow? Do most individuals in the population die at an early age or late in life? Study growth curves.
N = number of individuals in the population
t = time during which you take a measure of the population
N-t = number of individuals in the population when you measured the population at time "t".
- Exponential growth happens with no predators, lots of food and space to grow.
- Logistic growth happens when there is some limitation to growth (predators, space, etc.) -- uses "carrying capacity"
- Carrying capacity is the factor (called "K") that describes how big a population can grow.
If we could take a snapshot of a population at a certain time, what would the ranges of ages look like? Would there be lots of old individuals, or lots of young individuals? Survivorship curves describe the population.
- Tally up the individuals per age group or cohort. And age group can be "0-1 years old" or "0-20 years old".
- Take a population, count the individuals and keep track of number of individuals in the different cohorts.
- Survivors = the number of individuals that are alive (usually per age group). For example, there are 23,456 individuals from 0-1 years old in Columbia, MO.
- Make a plot for all the age groups (x-axis) with the number of individuals in each age class (y-axis).
- Plot the age cohorts so you can see the change in survivors as you go from age cohort to the next age cohort.
- The curve "Types" are plotted with the y-axis on a logarithmic scale. This makes the a straight line when the survivor group amounts change exponentially. When I say "change", I mean how does the number of survivors change from one age cohort to the next? If you line is above the theoretical straight line, then your population changes _less_ than exponential. If it's below the straight line, it changes _faster_ than exponential.
- "Exponential decrease" means that at each age interval, the amount of individuals dying is more than a fixed amount. A fixed amount would be like this: 100 people from 0-1 yrs old, then you have 98 people at 2-3 years old, then you have 96 people at 3-4 years old, etc. It's a fixed change of 2 individuals between cohorts.
Question: How do organisms with parental care affect the survivorship curves?
LAB 11 - Populations
Here is an audio file for Word on Macs: Population.docx
What and why of populations:
What?Why?
- Manage groups (conservation)
- Study population behavior (health, nature vs. nurture)
Mark-Recapture, Growth curves, Survivorship curves
How do we estimate the size of a population? Mark-recapture.
Capture and mark a smaller sample of the population, then re-capture and use this to estimate the total size.
Do populations grow fast or slow? Do most individuals in the population die at an early age or late in life? Study growth curves.
N = number of individuals in the population
t = time during which you take a measure of the population
N-t = number of individuals in the population when you measured the population at time "t".
- Exponential growth happens with no predators, lots of food and space to grow.
- Logistic growth happens when there is some limitation to growth (predators, space, etc.) -- uses "carrying capacity"
- Carrying capacity is the factor (called "K") that describes how big a population can grow.
If we could take a snapshot of a population at a certain time, what would the ranges of ages look like? Would there be lots of old individuals, or lots of young individuals? Survivorship curves describe the population.
- Tally up the individuals per age group or cohort. And age group can be "0-1 years old" or "0-20 years old".
- Take a population, count the individuals and keep track of number of individuals in the different cohorts.
- Survivors = the number of individuals that are alive (usually per age group). For example, there are 23,456 individuals from 0-1 years old in Columbia, MO.
- Make a plot for all the age groups (x-axis) with the number of individuals in each age class (y-axis).
- Plot the age cohorts so you can see the change in survivors as you go from age cohort to the next age cohort.
- The curve "Types" are plotted with the y-axis on a logarithmic scale. This makes the a straight line when the survivor group amounts change exponentially. When I say "change", I mean how does the number of survivors change from one age cohort to the next? If you line is above the theoretical straight line, then your population changes _less_ than exponential. If it's below the straight line, it changes _faster_ than exponential.
- "Exponential decrease" means that at each age interval, the amount of individuals dying is more than a fixed amount. A fixed amount would be like this: 100 people from 0-1 yrs old, then you have 98 people at 2-3 years old, then you have 96 people at 3-4 years old, etc. It's a fixed change of 2 individuals between cohorts.
Question: How do organisms with parental care affect the survivorship curves?